Extremity MRI allows office-based rheumatologists to diagnose rheumatoid arthritis early in its course and then to make clinical decisions as to whether to continue a given therapy, add an additional agent to the regimen, or switch to another agent, said Dr. Norman B. Gaylis, a rheumatologist in private practice in Aventura, Fla., who performs extremity MRI in the office.
Erosions and bone marrow inflammation can be seen on MRI but not on x-ray, which makes MRI a better tool for early diagnosis. “The other way in which I think in-office MRI is extremely helpful is to see whether the treatment is working or is not working,” said Dr. Gaylis. Treatment-related changes may not be apparent on x-ray for 2 years or longer. “That's a whole lot of time to be on a drug that is… very expensive and… maybe not working,” he said.
Standard MRI (0.75 tesla or greater) has been shown to be useful in diagnosing RA and for following therapy. The great demand for MRI on the larger machines that are based in hospitals and imaging centers results in long lead times for appointments. As a result, rheumatologists don't typically take advantage of this tool. In addition, patients with active RA sometimes find it intolerably painful to hold the position necessary for imaging in large machines.
Dr. Gaylis noted that extremity MRI (0.2 tesla) is performed in the office and allows for the patient to assume a more comfortable position during imaging. In addition, slices with this type of MRI average less than 1 mm and are contiguous, which is not always true of machines with stronger magnets. This can be important because it is possible for erosions to “hide” between the slices of larger machines, he added.
Extremity MRI is twice as sensitive as radiography in detecting erosions at baseline, according to a recent study by Dr. Gaylis and his colleagues (Mod. Rheumatol. 2007;17:273-8). In the study, 31 patients underwent both baseline extremity MRI and x-ray examinations. For 108 metacarpophalangeal joints, the sensitivity of radiography was 55.8%, compared with MRI, and specificity of radiography was 95.4%. Positive predictive value was 88.9% and negative predictive value was 76.5%.
In terms of in-office set up, smaller extremity MRI machines don't have many special requirements. Extremity MRI can be set up in a standard exam room. The floors need to provide sufficient support because the magnets are heavy. “One thing that you have to be careful of is that you have an environment where there is not that much noise [which interferes with the software],” said Dr. Gaylis. It's also important to keep the room cool because of the magnet.
Although the cost varies, in-office extremity MRI equipment costs around $250,000. However, the machines are typically leased, as are many other pieces of medical equipment, said Dr. Gaylis.
Once an extremity MRI is performed, Dr. Gaylis digitally sends the image to a radiologist, who reads the image and sends back a report, usually the next day. “I like this format because it combines my knowledge of the patient with the expertise of a musculoskeletal radiologist,” he said.
MRIs are more complicated to read than are x-rays because every joint imaged with MRI yields a number of slices. “So at the end of my day, after I've seen × number of patients, for me to go and read MRIs is really not practical,” said Dr. Gaylis. In addition, musculoskeletal radiologists have a high level of expertise in reading MRIs.
“At the end of the day, I think it allows me more credibility to say that my radiologist is reading it,” he said. The rheumatologist's responsibility is to react to the MRI findings and treat the patient appropriately, Dr. Gaylis noted.
Extremity MRIs can also help improve patient compliance. Patients can see the erosions for themselves. “When they see them and they understand why we want to put them through the process of a biologic … it absolutely makes the patient more responsive to [our] therapeutic suggestions,” said Dr. Gaylis.
The MRIs can also help keep patients on the right drugs. “They get a lot more understanding when they see an MRI that reflects what's going on,” said Dr. Gaylis.
Reimbursement of extremity MRI is a tricky subject, however. Even though extremity MRI is commonplace in the orthopedic setting, there is no reimbursement code that is specific to extremity MRI. Instead, codes for the larger conventional machines are used. Getting third-party payers to foot the bill for extremity MRI can be tough, but it can be done. “We've been able to show them that they actually would save money by getting [the patient] an MRI annually. If you give someone Remicade [infliximab] and it's not working … why not find out and stop it and stop paying all that money if it's not working,” said Dr. Gaylis. He estimates that 70% of his payers are paying for extremity MRI.